Description: (Verbatim from the applicant's abstract) An efficient method for solving the Poisson-Nernst-Planck (PNP) equations of electrodiffusion for arbitrary three-dimensional pore structures has recently been developed. PNP theory enables computation of ionic currents through biological ion channels that are embedded in lipid bilayer membranes under arbitrary conditions of inside/outside bathing solution concentrations and applied electrical potentials. This proposal presents plans to further develop PNP theory (e.g., when the permeant ion size is significant compared to pore dimensions), to speed-up the computer algorithm that is used to solve the PNP equations, and, especially, to apply the method to a variety of biological systems including gramicidin, several porins, and the nicotinic acetylcholine receptor. Biological ion channels play a fundamental role in physiological processes such as regulation of chemical concentrations, muscle contraction and signal transduction. The work proposed here will contribute to understanding of ion permeation through open channels, which is a critical aspect of the overall function of these devices.